Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. In use, an electrode is inserted into a major vein or artery, such as the femoral artery, and guided into the chamber of the heart which is of concern. Often, the target area of the heart is a tubular region, such as the pulmonary vein, the coronary sinus, the superior vena cava and the inferior vena cava.
Electrode catheters are used to identify and/or ablate tissue in the region of the heart exhibiting the aberrant electrical activity, Often, electrode catheters are capable of both mapping the tissue to locate the site of aberrant electrical activity, and ablating the identified tissue. The ablation of this tissue isolates this tissue from the rest of the heart, thereby preventing the aberrant electrical pathways from extending into other areas of the heart. One area of the heart where such ablation is typically desirable is the pulmonary vein. Several catheters, such as those described in U.S. Pat. Nos. 6,024,740 and 6,117,101, are designed to ablate circumferential lesions inside the pulmonary vein. These catheters comprise an ablation element, such as an ultrasound transducer, surrounded by an inflatable balloon. To ablate the desired circumferential lesion, the balloon is inflated to anchor the catheter within the pulmonary vein, and the transducer is activated to form a circumferential lesion in the tissue engaged by the balloon.
Although they are effective for creating circumferential lesions in heart tissue, these balloon catheters have several disadvantages. For example, the balloon often is situated incorrectly within the pulmonary vein and/or becomes dislodged from the anchoring site. Also, the balloon does not allow blood to flow past it, resulting in a build up of blood at the distal end of the balloon, causing the blood to clot. Accordingly, a mapping and/or ablation catheter having a stabilized anchoring mechanism that enables blood flow and prevents clots is desirable.